Radio frequency transmission line circuits



Aug. 12, f 19 T. M. GLUYAS, JR 2,606,964

RADIO FREQUENCY TRANSMISSION LINE CIRCUITS Filed Feb. 7, 1948 INVENTOR ATTO R N EY plirig device or 'balun.

Patented Aug. 12, 1952 S vTi? 1QUE. rror mmsmssimw; LINE- 1 s v v ignor :to :Radio Corporatiomof-iAmericma cor- 1-porati0n ofiDelaware ApplicationFebi-uary 7, 1e4fs s The present invention relates to radiofrequencY-transmission lines and more particularlyto transmission line arrangements for *couplin a single ended 01' unbalanced line to a balanced or push-pull transmission line arrangement.

'An o bject of the presentinventiomis the -provision-pf a wide band balance+to-unba1ance-:cou-

Another obj ectof *the; present invention {is the provision of means for coupling a; single ended or unbalanced transmission line to a pair'of transmission lines operating in-a balanced or push-pull relationship.

A further- 'object-of-the presentinvention Iis the provision of a coupling arrangement as aforesaid w hiclr'not only'is balanced overa-wide:band of frequencies, but which is also reflectionless over-'saidband.

-'--sti11 another object -of-- the---presentz invention isthe' provision of a'f 'balun operative-over-a wide band of-*frequencies. a The foregoing objects and 0thers--whioh: 'n1ay appear from the following detailed-description are attained by providing a :balance-toeunbal- 'ance coupling arrangementinawhich series me..- act-ance -are inserted .in: the: balanced line circuit to compensate for the: reactive comp'onentsiiritroducedin the coupling circuit as the frequency departs from 'the assigned value. 2 Thee-present invention-will be more fully understoodtby .reference to the following description which is. accompaniedbva'drawingin which: .1

Figure 1 illustrates; in sectional view, -a5' form 'ofbalance to-unbalance coupling deviceheretofore 'sknown ,in the prior .art; .-:whilelF!igure;2...il,

lustrates.inzdiagrammatic-jorm:anequivalent cirg .tirely closed except .where the various transmission lines enter. The. transmission-line imely-ineludes an inner conductor.lltiandaesurrounding ,outerusheath .2 2, while I lineTlla includes. an inner conductor 2| surrounded by...anotherl sheathl-fi. N

'ance converter to the load 15. I

The transmission line TLi has its outerishea th 12 extending into the-shell M aidistancee'qual to a: one-quarter of .the; operating rwavelength. Theinwardly extendin portion-of sheath:il'2z:.is identified by reference character 32. Ina coaxial end-to-end a'rran'gement with- .extension -"-32 :--is a cylindricalconductive member 3 3,:':-alsoone-quarter of 'the-1operatingmavelength longsan'd connectedat .its end remote from :the end of member-3.2 to outeivshell :14: 'The:iinner conductor fill. 'of transmissionrline' lLi-- extemis into the tubular memberrflg-a -idistance equalito one-quarter of t-he operatingewavelenfih and is terminated in :an electrical? open circuit. These members 3-2 and: 33 are electrically "j inverted images of one-another. At the adjacent ends of members 32 and 33.-at points A and =JB; of;.highest instantaneously:--equal and opposite apote'ntials, the conductors 20 and 2-I-ofthe balanced 'circuit are connected.

"The reactance provided :byzzthe tubular L condu'ctori33 i and ithe extension of inner conductor llfl githerewithin provides ra-i serie reacta'nce 1 elem'entLiXi', shown'diagrammatical-1y :ins. Figure-" 2, which over :a reasonably-wide bandofsfrequenciessnearlyccancelsztheireactiveecomponent:oL-the a-parallel .-.combinatiori. :formed byithe loagi.,;,| 5=rand the.iantiaresonantcircuits; :1 formed .:by--.:.conductors ;3.2 and; 3.3. withinpthe outershell 1.4. In Figuremthese reactances.areillustratedjndiagram- .matic; form as ireactances .....The :addednfeactance .IXJ. {10f Figure 2 representative otthe series 'reactance arof 'I=tubular:-.iconductor .133. zandqinner icondu'ctor I0-..a1so. acts.- tortune; out-.lany residual rearitancezim thegcircuitasuch as may. :becaused ..by the;.:sh0rtulhshifildfid lengths of conductors 1.0, -20;andszi;.;withinzthe:.shell .14. .These Ieactances arfe.indicatedziniFigurei,-.as.reactance-X4. New:aitzcaniibeaseen-ithat the;equivalentzcircuit rshowngin Eigure;.2 is; not completely: compensated. -If-;the.circuitszelements, indicated-by Xzladdgsus- :ceptan -.t the; loa'drztheiinput:resistanceizwill h v e :y iln owers han .thcload resistance; and i hessourcedmneziance:wfll:no;lon ershermatch d ibycethenloadaithus:causing.standingiwavesito -be set up in transmission line TL1. 'Ihisisz'true-even -thoughzsthe equivalent series .-react.ance 151.compensatedagby ;;;X1'. .;-In {order .:to.:.avoid;-.this.; unde- :sirable effect: he arr n ement; 'a cor inga-tmmy 2. An arrangement for coupling coaxial transmission line having center and TL: enters the tubular member 42 a distance 1 equal to one-quarter of the operating wavelength and is open circuited at the inner end thereof.

Similarly the conductor 21 enters tubular memsion line having an interruption in the sheath conductor at a point one-quarter wavelength at the operating frequency from the end thereof, said arrangement having a conductive shell substantially a half -wave long at said operating frequency surrounding said unbalanced coaxial transmission line at the end thereof and bein connected at each end to the sheath conductor thereof, two further sections of coaxial transmission line each having the sheath conductor connected to said shell at the ends thereof and being ber 43, a distance equal to one-quarter of the" operating wavelength and is open circuited at its inner end. Thus the reactance element formed by conductor 20 and tubular member 42 and the reactance element formed by conductor 2| and tubular member 43 are effectively in series with the load 15. At the operating frequency these open ended quarter wave lines act as though they were short circuited at the mouths of tubular members 42 and 43 and have no effect on the circuit. They are diagrammatically indicated as series resonant elements X3 in Figure 4.

Now. if at an arbitrary frequency removed from the midband frequency the reactance X3 is chosen approximately equal in value to the reactance'Xr, and the sum of the reactances of X1 and X3 is chosen equal in value to the reactance added by susceptance X2, the input at TL; will not only be non-reactive but will have a pure resistance value equal to a resistance of the load [5. Therefore, the network properly terminates the source, not only at the midband frequency but also at arbitrary frequencies above and below the mid-band frequency.

Thus the balance transformer of Figure 3 is not only balanced at all frequencies but is substantially non-reactive over a substantial band of frequencies. A band width at least thirty percent greater than obtainable with the structure of Figure l is thereby obtained.

' What is claimed is:

1. An arrangement for coupling an unbalanced coaxial transmission line having center and sheath conductors to a pair of transmission lines having inner and outer'conductors operating in balanced relationship, said unbalanced transmission line having an interruption in'the sheath conductor at a point substantially one quarter wavelength at the operating frequency from the end thereof, said arrangement having a. conductive shell" substantially a half-wave long at said operating frequency surrounding said unbalanced coaxial transmission line at the end thereof and bein connected at each end to the sheath conductor thereof, a further section of coaxial transmission line arranged within said shelLsaid further section of coaxial transmission line havmg interrupted sheath and center conductors, said interrupted sheath conductor being connected to said shell at the ends thereof and being connected to the interrupted sheath conductor of said unbalanced coaxial transmission line, the interrupted center conductor 'of said further coaxial transmission line having its adjacent ends connected to the inner conductors of said balanced transmissionlines, the outer conductors of said balanced transmission lines'being connected to said shell.

an unbalanced sheath conductors to a pair of transmission lines connected to the interrupted sheath conductor of said unbalanced coaxial transmission line on each side of the interruption, the other conductors of said further sections having adjacent ends connectedto the inner conductors of said balanced transmission lines, the outer conductors of said balanced transmission lines being connected to said shell.

3.. An arrangement for coupling an unbalanced transmission line to a balanced transmission line, including a conductive shell member, first, second; third and fourth sections of open-ended transmission line arranged within said shell member, said sections having a length substantially equal to a quarter wavelength at the operating frequency, each of said sections having one end of one conductor thereof connected to said shell member, the other end of said one conductor of said first section being connected to the other end of said one conductor of said third section and the other end of' said one conductor of said second section being connected to the other end of said one conductor of said fourth section, the other conductors of said first and said second sections being connected in series, means to connect said unbalanced transmission line to the conductors of said first section at said oneend thereof, and means to connect said balanced transmission line to the other conductors of said third and said fourth sections at said other ends thereof. I

4; An arrangement for coupling an unbalanced coaxial transmission-dine to a pair of coaxial transmission lines operating in balanced relationship, said coaxial transmission lines having center and sheath conductors, said arrangement including a conductive shell member, first, second, third and fourth sections of open-ended coaxial transmission line having inner and outer conductors arranged within said shell member, said sections having a length substantially equal to aquarter wavelength at the operating frequency, each of said sections having one end of the 'outer'conductor thereof connected to said shell member, the other end of the outer conductor of said first'section being connected to the other end of the outer conductor of said third section and the other end of the outer conductor of saidsecond section being connected to the other end of the outer conductor of said fourth sectionJth inner conductors of said first and second sections being connected in series, means to connect the sheath conductors of said coaxial transmission lines to said shell member, means to connect the center conductor of said unbalanced transmission line to the inner conductor of said'first section at said one end thereof, and means to connect the center conductors of said balanced transmission lines individually to the inner conductors of said third and said fourth sections at said other ends thereof.

two-conductor transmission line to a transmission line arrangement having at least two con 5 ductors operating in balanced relationship, said arrangement including a conductive shell member, first. second, third and fourth sections of open-ended coaxial transmission line having in- Her and outer conductors, arranged within said shell member, said transmission line sections hav- 7 ing a length substantially equal to a quarter wavelength at the operating frequency, each of said transmission line sections having one end of the outer conductor thereof connected to said shell member, the other end of the outer conductor of said first transmission line section being connected to the other end of the outer conductor of said third transmission line section and the other end of the outer conductor of said second transmission line section being connected to the other end of the outer conductor of said fourth transmission line section, the inner conductors of said first and said second transmission line sections being connected in series, means to connect the conductors of said unbalanced transmission line to the conductors of said first transmission line section at said one end thereof, and means to connect said two balanced conductors of said transmission line arrangement individually to the inner conductors of said third and said fourth transmission line sectionat said other ends thereof.

6. An arrangement for coupling an unbalanced concentric transmission line to a pair of coaxial transmission lines operating in balanced relationship, said concentric transmission line comprising inner and outer conductors and said coaxial transmission lines comprising central and sheath conductors, said arrangement including a conductive shell connected to said sheath and said outer conductors of said transmission lines, the connection to said outer conductor of said concentric transmission line being made at a distance from the end thereof substantially equal to a quarter wavelength at the operating frequency, a plurality of open-ended transmission line sections having lengths substantially equal to a quarter wavelength at said frequency and comprising tubular conductors and central conductors arranged within said tubular conductors, one of said transmission line sections having the tubular conductor thereof connected to said shell at one end of said section and having the central conductor connected at the other end of said section to the inner conductor of said concentric transmission line, another of said transmission line sections having the tubular conductor thereof connected to the outer conductor of said concentric transmission line and still another transmission line section having the tubular conductor thereof connected to the tubular conductor of said one transmission line section, the central conductors of said coaxial transmission lines being connected to the central conductors of said other transmission line sections.

7. An arrangement for coupling an unbalanced concentric transmission line to a pair of coaxial transmission lines operating in balanced relationship, said concentric transmission line comprising inner and outer conductors and said coaxial transmission line comprising central and sheath conductors, said arrangement including a conductive shell, connected to said sheath and said outer conductors of said transmission lines, the connection to said outer conductor of said concentric transmission line being made at a distance from the end thereof substantially equal to a quarter wavelength at the operating frequency, a plurality of tubular conductors arranged within said shell, one of said tubular conductors being connected to said shell at one end, the inner conductor of said concentric transmission line extending within said one tubular conductor for a distance substantially equal to a quarter wavelength at the operating frequency, another of said tubular conductors being connected to the outer conductor of said concentric transmission line and still another of said tubular conductors being connected to said one tubular conductor, the central conductors of said coaxial transmission lines extending within said other tubular conductors for a distance substantially equal to a quarter wavelength at said frequency.

8. An arrangement for coupling an unbalanced coaxial transmission line having center and sheath conductors to a pair of transmission lines having inner and outer conductors operating in,

balanced relationshi including a conductive shell substantially a half-wave long at the operating frequency, two pairs of tubular conductive members arranged within said shell, the members of each pair being arranged in end-toend relationship relative to each other and the ends of said members remote from the adjacent ends being connected to an end of said shell, the adjacent ends of one pair of said conductive members being connected to the corresponding adjacent ends of the other pair, the sheath conductor of said unbalanced line being connected to said shell to form a continuation of one of said members and the inner conductor thereof being extended into said one member and its complementary member, the inner conductors of said balanced transmission lines being extended individually into the members of the other pair of said members, and the outer conductors of said balanced transmission lines being connected to said shell.

THOMAS M. GLUYAS, J R.

REFERENCES CITED The following references are of record in the file of thispatent:

UNITED STATES PATENTS Goldmann Aug. 24, 1943 p 

